Solid-state lighting dimmers operate by essentially restricting the average current flow through a load by means of controlling the conduction of the load current through a device such a triac or some other switching semiconductor device like a Metal-Oxide Semiconductor Field-Effect Transistor (MOSFET) or Bipolar Junction Transistor (BJT). The longer the triac or switching semiconductor is allowed to conduct in each AC cycle, the more average current is provided to the load. The “off” state is when the triac is not allowed to conduct at all, but even though a light bulb will appear to be completely off in this state, there is measurable leakage current through the triac.
Some configurations of electronically controlled dimmers have included a microcontroller that may monitor the AC mains, control the triac, support wireless communications, control a relay that provides an air-gap safety function, and provide other dimmer features. This processor-controlled system works well as long as the microcontroller in the dimmer is always powered and active, meaning the dimmer is always receiving AC power. The dimmer microcontroller can receive a generally consistent power flow in cases when a neutral wire is available in the wall box in which the dimmer is installed. The availability of the neutral wire allows power to be supplied to the microcontroller and lighting load simultaneously. In other words, a parallel wiring configuration is possible when the neutral wire is available.
However, it is common to have wiring situations where a neutral wire is not available at the location where the dimmer will be installed (e.g., the wall box). In these situations, the dimmer is not powered in parallel with the hot and neutral AC wires but in series with the hot and load wires. For series connections, another type of power supply system (i.e., a load controlling and line monitoring system) is needed to power the dimmer and also properly control the load. In essence, the “load-line-powered” dimmer's power supply steals some of the current for a limited time period from the hot lead to power its own processing circuitry, while its power supply return path is actually through the load.
Of course, if this load-line-powered dimmer's power supply return path is opened for any reason, the dimmer is shut off. This is the same as if a power switch shut off the dimmer's power supply circuitry. Once the dimmer's microcontroller is shut off, the microcontroller may reset itself or otherwise operate improperly.
Another problem with the configurations described above is that manufacturers of solid-state dimmers have needed to supply two types of solid state dimmers. One type of available dimmer is capable of operating properly in a parallel wiring configuration where a neutral line exists. Alternatively, another dimmer configuration is manufactured to contain the proper circuitry to operate in series with the load and power the microcontroller using a limited portion of the AC cycles received by the dimmer. Manufacturing and stocking inventory for both types of solid state dimmers tends to add complexity to the supply chain and increase the volume of product returns.
In addition, installers of the devices in the field are in a position where they end up carrying both types of solid-state dimmers in order to be prepared to properly install dimmers regardless of whether a neutral line is available. This situation increases the number of dimmers that are carried by installers and can also increase the amount of product returns when the incorrect number of a specific dimmer type is ordered.